Field of the Invention
The present invention relates to a method and apparatus for configuring information efficiently in logging channel measurement information in a mobile communication system. In more particular, the present invention discloses a terminal operation of indicating to a base station whether the measurement has been performed to a serving cell or neighbor cells for configuration of the channel measurement information. Also, the present invention proposes a method for a terminal to adjust the frequency of log in consideration of the importance of the measurement information.
Description of the Related Art
Typically, the mobile communication system has been developed for the user to communicate on the move. With the rapid advance of technologies, the mobile communication system has evolved to the level capable of providing high speed data communication service as well as voice communication service. Recently, the 3GPP, as one of the next generation mobile communication standardization organizations, is in the progress of standardization of Long Term Evolution-Advanced (LTE-A). LTE-A is one of the high speed packet-based communication technologies supporting data rate higher than that of the current mobile communication technology under the objective to complete the standardization in late 2010.
With the evolvement of the 3GPP standard, many discussions are being conducted for optimizing the radio network in addition to the effort for increasing data rate. In the initial radio network configuration or optimization stage, a base station or a base station controller should collect radio environment information related to its own cell coverage, and this process is called Drive Test. Since the conventional drive test is performed in such a way that an operator carries the test apparatuses on a vehicle while performing the measurement task repeatedly for long time. The measurement result is used to configure the system parameters of the base stations or base station controllers. Such a conventional drive test increases total costs and time of the radio network optimization and maintenance. Study on minimization of drive tests and enhancement of radio environment analysis process and manual configuration is being conducted in the name of MDT (Minimization of Drive Test). In order to accomplish the aforementioned purposes, the UE measures radio channels and reports the radio channel measurement information to the eNB periodically at an interval or immediately in response to a specific event or after a predetermined time has elapsed from the time point when the radio channel measurement information has been recorded, instead of performing the drive test. In the following description, the process for the UE to transmit the radio channel measurement information and other supplementary information to the eNB is called MDT measurement information report. In this case, the UE reports the channel measurement result immediately right after the completion of channel measurement in a state where the communication is available with the eNB but deters the report in a state where the communication is not available with the eNB until the connection to the eNB is recovered. The eNB uses the MDT measurement information received from the UE for cell coverage optimization. In LTE-A, basic MDT measurement information report operations are classified according to the UE RRC state as shown in table 1.
TABLE 1UE MDT measurement UE RRC stateinformation report operationIdle modeLogging and deferred reportingConnected modeImmediate reportConnected modeLogging and deferred report
Table 1 shows the basic MDT information report operation depending on the RRC state of the UE.
In table 1, if the UE is not communicating with the eNB, the UE is in the idle mode and, otherwise, in connected mode. In the case of MDT, the channel information measured by the UE is supposed to be transmitted through RRC signaling such that, although the UE is in the idle mode, it is not necessary to transition to the connected mode for information transmission. In this case, the UE logs the channel measurement information and defers the transmission of the information until it transitions to the connected mode.
Although if necessary it is possible to transmit the channel measurement information to the eNB immediately even in the connected mode, the UE can defer the transmission of the measurement information logged in the idle mode until it transitions to the connected mode. The eNB requests for the measurement information report such that the corresponding UE transmits the logged measurement information.
The UE in the idle mode logs channel measurement information periodically or when a certain event triggering channel measurement information log occurs. The exemplary channel measurement information log-triggering events are as follows.
(1) Periodic downlink pilot measurement
(2) Serving Cell becomes worse than threshold
(3) Transmit power headroom becomes less than less than threshold
(4) Paging Channel Failure
(5) Broadcast Channel failure
(6) Random access failure
(7) Radio link failure report
It is expected that the MDT measurement and log information configuration method is defined by taking notice of the conventional RRC measurement method. However, unlike the conventional RRC measurement method perform with the assumption of the existence of a serving cell, the MDT measurement is performed regardless of the existence of serving cell. This is because since the MDT measurement information is supposed to be used for cell area optimization other than supporting mobility the UE has to measure the signals from the adjacent eNBs even in service coverage hole. In the RRC measurement procedure, the measurement result report includes the serving measurement result and neighbor cell measurement results. If this operation mechanism is applied to the MDT measurement report without modification, it may fail logging the serving cell measurement information in a certain case, resulting in confusion. There is therefore a need to define a detailed operation for this.
The convention RRC measurement method is provided with an algorithm for limiting the cell measurement range in order to minimize the power consumption of the UE in the idle mode. The RRC measurement aims to check the signal qualities of the neighbor cells as well as the serving cell in order for the UE to attach to the best cell. If the condition of the serving cell lower than a predetermined threshold and a neighbor cell has the better signal quality, the UE attempts access to the corresponding cell. If the signal quality of the serving cells is equal to or higher than the threshold, there is no need of checking the signal condition of neighbor cells consuming UE power unnecessarily. Accordingly, if the signal strength of the serving cells is equal to or greater than a predetermined threshold, no neighbor cell signal measurement is performed in the RRC measurement method. The UE selects the neighbor cell for measurement in stepwise manner using two threshold values of Sintrasearch and Snonintrasearch.
FIG. 1 shows a UE measurement operation in the idle mode according to two threshold values. If the Reference Signal Received Power (RSRP) 115 of the serving cell is greater than Sintrasearch 105, the UE does not measure the signals of neighbor cells. This is because the current serving cells has the signal quality good enough. Otherwise, if the RSRP of the serving cell is equal to or less than Sintrasearch 105 and greater than Snonintrasearch 110, the UE measures the signals of the neighbor cells operating on the same frequency of the serving cell. if the RSRB of the serving cell is less than Snonintrasearch 110, the UE measures the signals of cells operating on other frequencies and other systems.
The MDT measurement method is likely to be designed to operate in similar manner to the RRC measurement method and employ the two threshold values of Sintrasearch and Snonintrasearch, as they were, to reduce power consumption of the UE. However, since the MDT measurement is focused on the cell area optimization other than mobility support, there is no need of knowing why there is no measurement result of the neighbor cells in the log unlike the conventional RRC measurement. This means that there is a need of the information indicating the reason of the absence of measurement result, i.e. whether the measurement result is absent due to the signal strength of the serving cell which is good enough or the measurement to the neighbor cells is not performed actually.
Meanwhile, the location information is one of the important elements in MDT measurement. It fails to receive GPS-based location information, the UE measures a set of the received signal strengths from neighbor eNBs and sends the measurement result to the serving eNB. The eNB calculates an approximate measurement location using the triangulation with the received signal strength set received form the UE. If the RSRP of the serving cell is greater than Sintrasearch, there is no chance to measure the neighbor cells and thus it is impossible to measure and log a set of the signal strengths of the neighbor cells for use in location information acquisition. At this time, since the MDT measurement without location information degrades the usability, it is not preferred to perform logging periodically and thus increase the UE and signaling overheads.